Conventionally, an engine of a small displacement is often employed as a power source of a portable work machine such as a chainsaw. Power from such an engine is transmitted via a centrifugal clutch to a sprocket around which a saw chain is wounded. Among a variety of centrifugal clutches that have been developed, a pendulum centrifugal clutch including: a hub fixed to an output shaft of the engine; a pair of arms integrally provided to the hub; a boss provided to a distal end of the arm; and a shoe rotatably fitted to the boss is known as a centrifugal clutch applied to a portable work machine, of which downsizing and weight reduction are desired (e.g., Patent Document 1).
The centrifugal clutch disclosed in Patent Document 1 does not employ conventional locking means such as an E ring to prevent the shoe from disengaging from the boss. Instead, the centrifugal clutch employs a projection integrally provided to the boss, thereby omitting separate members such as locking means and decreasing the number of means.
Patent Document 1: JP-A-07-190100